In an air conditioner of this type, it is important to detect and control a circulation amount of refrigerant flowing in a refrigerant circulation circuit, i.e. a refrigerant circulation amount. Japanese Patent Application Publication No. 2001-140767, for example, discloses an air conditioner wherein two pressure monitoring points are provided in a refrigerant circulation circuit including a variable capacity compressor, and a refrigerant circulation amount is controlled using a correlation between a differential pressure between those pressure monitoring points, and the refrigerant circulation amount. Specifically, the differential pressure between the pressure monitoring points is detected, and a discharge capacity of the variable capacity compressor is feedback controlled so that the detected differential pressure approaches a control target value.
For stably executing the feedback control, it is essential to detect the differential pressure between the two pressure monitoring points with high accuracy. For improving the detection accuracy of the differential pressure, it is considered to prolong a distance between two pressure monitoring points 2 and 3 in a refrigerant circulation circuit 1 as shown in FIG. 1, or to provide a restrictor 4 in the refrigerant circulation circuit 1 as shown in FIG. 2. In the former case, either one of two conduit portions 6 and 7 for introducing pressures at the pressure monitoring points 2 and 3 to a differential pressure sensor 5 is made longer and, resultantly, an air conditioner becomes complicated. In the latter case, a pressure loss is generated due to the restrictor 4 so that the efficiency of the air conditioner is lowered.
For enabling the feedback control, the variable capacity compressor is provided with a control valve driven by an electromagnetic force. In order to use the foregoing differential pressure as a force to directly counter the electromagnetic force of the control valve, a pressure transmitting passage becomes necessary for introducing the pressure at one of the two pressure monitoring points to the variable capacity compressor. Such a pressure transmitting passage makes intricate a design for the variable capacity compressor.
It is therefore an object of the present invention to provide an air conditioner that can control a refrigerant circulation amount in a refrigerant circulation circuit with a simple structure and without lowering the efficiency.